Natural left-handers should always be left to develop in their own way and be allowed to write left-handed if that is their choice. Forcing them to change hands and write right-handed can have very bad effects in later life as well as being traumatic at the time and ruining their handwriting!
The dominant writing hand is not just a physical thing to do with controlling a pen but a mental thing to do with the way the brain is organised and where certain functions occur. The brain is “cross-wired” to the body so the left handed side of the brain controls the right hand side of the body and the right side of the brain controls the left. Changing the hand used for writing causes great confusion in the brain and can have a lot of knock-on effects.
– See more at: http://www.anythinglefthanded.co.uk/being-lh/children/changing-left-to-right.html#sthash.YZjf8h5V.dpuf